I was at least ranked gold in almost every made of the arena, even diamond in one of them. But today I’ve seen that I now have to play the 10 matches to get ranked again. I’ve restarted my xBox one by pressing the power button for 10 seconds, but even now my rank is gone 
please help me 
This was a planned rest of everyone’s rank, it’s for the the start of the new season. More details on seasons are in this blog post
Thank you very much for your fast answer 